Tunnel workers often engage in activities in a high pressure environment, for example, a tunnel extending beneath a body of water or a tunnel extending into and through a mountain. Tunnel pressures in these environments often range as high as about 50 psig; and at pressures above about 11 psig, the tunnel workers are typically subjected to a daily compression/decompression cycle between tunnel pressure and atmospheric pressure.
Tunnel workers, whether they work in a high pressure environment or not, typically follow a similar schedule. They work an eight hour shift; and if they are working at high pressures, a portion of the shift is spent in compressing from atmospheric pressure to the working pressure and another portion of the shift is spent in decompressing from the effects of high pressure according to readily available schedules or tables. However, repeated full decompression after each work period is time consuming, may provide the worker with a psychological crutch tending to promote absenteeism, and necessarily limits the effective work output per man-day by limiting the number of working hours per "eight hour work day." In addition, repeated full decompression exposes the worker to a higher incidence of the bends and is believed to result in a higher incidence of bone related diseases, for example, osteonecrosis bone neurosis.
By borrowing from deep water diving technology, one might have expected that the effects of repeated full compression/decompression cycles could be successfully avoided. That technology teaches that the worker should be maintained at or near the high pressure found at the work area for an extended period of time, including non-work or "rest times." However, these diving systems have generally been directed to work activities at a depth of up to 1000 feet or more, where working pressures may be as great as 400 or more psig. Thus, while such systems have proven feasible and successful in connection with deep water projects, they still provide a relatively long decompression time when the worker leaves the pressure system because a full decompression from substantially the working pressure is still required. Thus the tendency to have adverse reactions such as the bends and increased incidence of bone related disease persists. The problem is compounded because the tunnel worker, unlike the diver, does not "stay under" until the job is done. Instead, he continues to work substantiall his usual "work week." Additionally divers generally work in small groups, three to six man crews, whereas tunnel workers typically work in larger groups, for example, crews of twelve men or more.
Consequently, the problem of repeated substantially full compression/decompression from tunnel work areas having high pressure environments remains and workers must either engage in work activities at high pressures less often or ignore the problems of repeated substantially full compression/decompression.
It is therefore a principle object of this invention to provide a method and apparatus for allowing tunnel workers to engage in high pressure work activities without subjecting them to the increased risk of bone related disease. Other objects of the invention are to provide an efficient work structure whereby tunnel work in a high pressure environment may continue on a twenty-four hour basis, if desired, to increase work productivity, to provide apparatus which is relatively simple in structure and easy to maintain, to provide comfortable rest facilities for the tunnel workers, and to provide reliable apparatus capable of performing its function over long periods of time.
A further object of the invention is to avoid a substantially full decompression from the tunnel pressure.